In a machine, such as a motor grader, for example, an engine and a transmission work together to propel the machine and operate implements, such as a motor grader blade. A gear shift lever is used to select a gear for operating the machine from among a number of forward and reverse gears. Sometimes, when roading, which is moving the motor grader with the blade off the ground, especially when roading downhill, it is possible for the transmission speed to exceed the speed desired for the present gear of the transmission. Such a condition is called an overspeed condition because the transmission overspeeds its gear. It is also possible to have an engine overspeed condition. Overspeed conditions exist outside the range of optimum operating speeds for the machine and cause a decrease in the efficiency of operation and may damage the machine. Overspeed conditions are therefore undesirable. Accordingly, it will be appreciated that it would be highly desirable to control overspeed conditions and prevent damage or excessive wear of the machine.